According to a color display apparatus which is currently widely used, three primary colors (red (R), green (G), and blue (B)) are employed as one set and light quantities of the respective colors are adjusted to perform additive color mixing, thereby realizing color display.
Display is obtained as a group including light emission portions and non-light emission portions in a plurality of pixels. Each of the pixels has a sub pixel for emitting a red color (hereinafter, referred to as R sub pixel), a sub pixel for emitting a green color (hereinafter, referred to as G sub pixel), and a sub pixel for emitting a blue color (hereinafter, referred to as B sub pixel), that is, sub pixels for three primary colors. Various three-primary-color disposition methods have been proposed up to now. Known dispositions are as follows. For example, as illustrated in FIG. 11, there is a stripe disposition in which an R sub pixel, a G sub pixel, and a B sub pixel are repeatedly disposed in a horizontal direction and respective sub pixels are adjacent to each other in a vertical direction. As illustrated in FIG. 12, there is a mosaic disposition in which an R sub pixel, a G sub pixel, and a B sub pixel are repeatedly disposed in the horizontal direction and the respective sub pixels are disposed in the vertical direction so as to be offset with respect to each other by 1 pitch. As illustrated in FIG. 13, there is a delta disposition in which an R sub pixel, a G sub pixel, and a B sub pixel are repeatedly disposed in the horizontal direction and the respective pixels are disposed in the vertical direction so as to be offset with respect to each other by ½ pitch. Incidentally, the terms “horizontal direction” and “vertical direction” herein employed merely indicate directions in the drawing plane of the figure. In other words, the directions do not indicate the horizontal direction and the vertical direction of an actual display apparatus and may be reversed according to the type and manner of usage.
In addition to the above-mentioned dispositions, various dispositions are disclosed, for example, in Japanese Patent Application Laid-Open No. S61-056304.
In recent years, there has been a high-definition display apparatus whose resolution exceeds 200 ppi. In addition to the design of pixel and sub pixel disposition, reduction in pixel size and sub pixel size has proceeded. Therefore, a further increase in resolution has been desired.
When a higher-definition image is to be displayed in the conventional pixel disposition to satisfy the demand for the increase in resolution of the recent display apparatus, it is necessary to increase the number of pixels in a display region of the display apparatus. Therefore, a further reduction in pixel size is required.
However, when the conventional pixel size is to be further reduced, several adverse effects may be caused. For example, in the case of a display apparatus using a liquid crystal or a display apparatus using an organic EL material, there is a reduction in pixel aperture ratio. Even when the pixel size becomes smaller, the width of a wiring pattern for driving R, G, and B sub pixels included in each pixel does not change. Therefore, when a pixel area is reduced, the pixel aperture ratio, that is, a surface area of a pixel to a total area of a display region becomes smaller, so that the brightness of the display region reduces.
In the case of the organic EL device, when the respective sub pixels are to be separately formed by, for example, a vacuum evaporation method using a mask, the reduction in the size of each of the separately formed sub pixels, which corresponds to the reduction in pixel size, is made, therefore, the opening size of the mask needs to be reduced. For example, in the case of a display apparatus whose resolution in the horizontal direction is of 300 ppi, the pixel pitch in the horizontal direction becomes a small value of approximately 90 μm.
In the case of the stripe disposition illustrated in FIG. 14A, the sub pixel pitch is 30 μm as illustrated in FIG. 14B, so that the opening width of the mask is equal to or smaller than the sub pixel pitch. It is extremely difficult for the current technology to obtain the opening width by using a metal mask thin plate for etching. Even when the stripe disposition is provided by a plating method using a photolithography technique, it is necessary to generally ensure a mask evaporation deviation amount of ±10 μm in view of the opening precision and opening position precision. In the case of the stripe disposition illustrated in FIG. 14A, the interval between adjacent sub pixels in the horizontal direction is ensured to be 20 μm in view of the mask evaporation deviation amount and the driving wiring pattern. In this cases the pixel aperture ratio is extremely small. When the pixel aperture ratio reduces, the brightness of the display region can be maintained by increasing brightness of the sub pixels corresponding to the reduction in the pixel aperture ratio. However, particularly, in the case of the organic EL device, an adverse effect such as shortening of a life thereof, which corresponds to the increase in brightness, can be generated. Therefore, it is important to maximize the pixel aperture ratio when the display apparatus is designed.
Another method of increasing the resolution is a method of disposing, in each pixel, a plurality of G sub pixels having the highest visual sensitivity among the three-primary-color sub pixels as described in Japanese Patent Application Laid-Open Nos. H02-000826 and S59-111196. In a color display apparatus described in Japanese Patent Application Laid-Open No. S59-111196, an R sub pixel, a B sub pixel, and two G sub pixels are disposed in each pixel. The area of each of the G sub pixels is set to ½ of an area of each of the R sub pixel and the B sub pixel.
However, as illustrated in FIGS. 15A and 15B, when the number of G sub pixels in each pixel is merely increased, the pixel size increases (X0<X1), so that there is the case where the resolution is not increased as large as expected. Therefore, as illustrated in FIG. 16B, a method of reducing the size of the G sub pixel is disclosed.
However, even when the size of the G sub pixel is reduced, it is unavoidable that the pixel size in the disposition illustrated in FIG. 16B becomes larger than a pixel size in an RGB stripe disposition illustrated in FIG. 16A (X0<X1) because of the limit of the driving wiring pattern. As a result, a problem of the reduction in pixel aperture ratio and a problem of the difficulty of sub pixel patterning occur.
Even in the case where an R sub pixel, a B sub pixel, and two G sub pixels are disposed in each pixel as described in Japanese Patent Application Laid-Open No. S59-111196, when a higher-resolution image is to be displayed, a suitable disposition is required in view of sub pixel dispositions of adjacent pixels. A displayed image is evaluated in each of the horizontal direction, the vertical direction, and the oblique direction. In order to obtain higher resolution feeling, it is necessary to uniformly distribute the R sub pixels, the G sub pixels, and the B sub pixels in any of the horizontal direction, the vertical direction, and the oblique direction. According to the color display apparatus described in Japanese Patent Application Laid-Open No. S59-111196, although the two G sub pixels are disposed in each pixel to improve the resolution feeling, the disposition in which higher resolution feeling is obtained for each of the R sub pixel, the G sub pixel, and the B sub pixel is not made. When each G sub pixel is not adjacent to other G sub pixels as with the case of the color display apparatus described in Japanese Patent Application Laid-Open No. S59-111196 (see FIG. 3(2)), each G sub pixel is smaller than the conventional G sub pixels. Therefore, there is posed a problem that sub pixel patterning becomes more difficult because of the deviation of patterning position.